[Amps] How to know when filter caps begin to fail

[TexasRF at aol.com]

Hi Carl, as you know, there are only eight of those filter C's in the  
Ameritron amps. When AC line voltage gets up around 245vac or so, the unloaded  
plate voltage gets close to 3600vdc. That leaves very little or no headroom 
with  a string of 450v caps, let alone ones that top out at 440v.
 
I learned all about this the hard way when an AL1500 was strapped for  
200vac operation in an attempt to get more power output.
 
Not a pretty sight! Dumb! Dumb! Dumb!
 
73,
Gerald K5GW
 
 
 
 
 
 
In a message dated 3/28/2012 8:12:58 P.M. Central Daylight Time,  
km1h at jeremy.mv.com writes:

After a  short time reforming of modern caps anything over 1ma at 450V I 
consider  junk.
Ive also rejected new caps that started acting up at around 440V  which 
caused Ameritron grief when I told them. They found out their  supplier was 
short changing them on the aluminum and have been  testing....and rejecting 
since.

I buy large amounts of repair parts  from them so they listen when I report 
a  
problem.

Carl
KM1H



----- Original Message -----  
From: "Gene May" <gene-may at hotmail.com>
To: "Amplifier Mailing  List" <amps at contesting.com>
Sent: Wednesday, March 28, 2012 8:19  PM
Subject: Re: [Amps] How to know when filter caps begin to  fail


>
>
> 1.  I, too, have shared Bob K6UJ's  experience with an electrolytic cap 
> exploding, and the mess was awful  enough to make me conservative about 
the 
> issue of replacement.   The goo between the foil seems to be somewhat 
> corrosive, was slow to  clean off, and  damaged some of the metal it got 
>  on.
>
> 2.  I'm cheap, and have used many surplus  electrolytic caps.  Along with 
> Glen K9STH's suggestions, I  suggest that anyone also using surplus caps 
> connect them in series  and place some DC across for a few hours, then 
see 
> how much they  leak.  I toss anything that gives off any more than a few 
> watts  -- I've seen leakages of 20 - 30 mA at voltages of around 300V (6 
- 
> 9  watts) on surplus caps -- and know others who are even more 
conservative  
> than I about throwing them out.  They can be so much cheaper  than new 
that 
> I think it is cheap insurance being conservative.   Along with Glen, I 
have 
> found that frequent usage tends to make  electrolytic caps last longer, 
not 
> go bad faster.
>
>  3.  Finally, particularly if you use surplus caps, I suggest that AFTER  
> THE CAPS ARE THOROUGHLY DISCHARGED, every so often it is worthwhile  to 
> simply feel them after they have been under power for a few hours,  and 
> replace the whole batch if any one of them is particularly  warm.
>
> Gene May
> WB8WKU
>
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